1. Field of the Invention
The subject invention is related to automotive gasket technology, and more particularly, to a multiple layered embossed metallic gasket assembly and a method of constructing the same.
2. Background of the Related Art
Metal gaskets are traditionally used to form a seal between two mating components of a mechanical system or device such as an internal combustion engine, to prevent leakage of combustion gases, cooling water, lubricating oil, or the like. Common applications involve placement of a gasket between the engine block and cylinder head, and between the cylinder head and exhaust manifold. Cylinder head gaskets typically extend around the cylinder bores of an engine to seal high pressure combustion gases within the cylinder bores, as well as seal oil and coolant passages. Exhaust manifold gaskets typically extend around the exhaust ports of an engine to seal high temperature exhaust gases flowing into the exhaust system. Once installed, the gasket bears the load from a bolted connection of the engine components and relies upon this load to provide an adequate seal therebetween.
To function as a reliable seal, it is known to provide a raised bead on a metal gasket in the area which surrounds a cylinder bore or exhaust port. The bead elastically deforms by tightening a bolt connection, and the elastic restoring force of the bead provides the required sealing effect. It is also known in the art to limit the compression of the raised bead by folding over a portion of the gasket adjacent the bead to function as a shim. In the absence of such a shim, when the gasket is tightened, the bead could be compressed beyond the elastic limits of the gasket material, resulting in an ineffective seal.
An example of a prior art metal gasket having specific structure to prevent over-compression of a resilient sealing bead is disclosed in U.S. Pat. No. 5,431,418 to Hagiwara et al. The gasket includes first and second opposed metal plates each having at least one opening with a surrounding bead. The plates are disposed in parallel such that the beads face each other, and an annular metallic shim is secured to the first plate adjacent the outer periphery of the bead, and is of a greater thickness than the bead, so that when a compressive load is applied to the gasket, both beads can only be deformed until their combined height equals the thickness of the shim. Hagiwara et al. disclose that the shim is welded by laser to the first plate around the opening to form a continues weld zone around the periphery of the shim. In the harsh environment of an internal combustion engine, wherein components are continuously subjected to high mechanical stresses, the weld zone could become an area of mechanical failure. In addition, the laser welding process will necessarily increase the overall manufacturing and labor cost associated with assembling the gasket.